I had a case a few months back where I’d determined that QoS was screwing over some network connectivity on a Server Core install. On a full install I’d simply use ncpl.cpl and remove the QoS Packet Scheduler binding from the adapter. Not so on the Core install. I had to resort to some registry hacking to disable the QoS Packet Scheduler to resolve my problem.
Download links are here:
NVSPBind - http://code.msdn.microsoft.com/nvspbind
NVSPScrub - http://code.msdn.microsoft.com/nvspscrub
NVSPScrub helps restores your virtual networking configuration if you happen to screw it up with NVSPBind! :-)